Vehicles may include cooling systems configured to reduce overheating of an engine by transferring the heat to ambient air. Therein, coolant is circulated through the engine block to remove heat from the hot engine, and the heated coolant is then circulated through a radiator near the front of the vehicle. Heated coolant may also be circulated through a heat exchanger to heat a passenger compartment. The cooling system may include various components such as various valves and thermostats.
The various cooling system components may need to periodically diagnosed. For example, if even one of the cooling system valves is degraded, it may not be clear whether an increase in coolant temperature is due to a change in valve position or due to an unexpected overheating of an engine system component. As such, various diagnostic routines may be used, such as those that monitor changes in temperature (e.g., changes in coolant temperature and/or transmission oil temperature) to diagnose the various cooling system valves. However, the inventors herein have recognized that the reliability of the test results may vary based on engine conditions. For example, the same test may be more reliable during warmer engine conditions (e.g., after engine warm-up is completed) as compared to cooler engine conditions (e.g., before or during engine warm-up). The test results may further vary based on cabin heat losses being incurred at the time of testing.
In one example, some of the above issues may be addressed by a method comprising, heating a transmission by flowing coolant through a first loop while stagnating coolant in a second loop of a cooling system, the first loop including an engine and a first valve, the second loop including the transmission and a second valve. Then, after a transmission oil temperature is raised by a threshold amount, indicating cooling system degradation based on an expected transmission oil temperature relative to an estimated transmission oil temperature. In this way, conditions that favor more reliable test results may be actively created and diagnostic routines may be performed only during conditions when the estimated temperatures are reliable.
For example, during selected conditions, a position of a bypass shut-off valve and a heater shut-off valve may be adjusted to vary an amount of coolant that is stagnated at the engine block and heater core, while also controlling a temperature of coolant circulated at a cooling system thermostat. By stagnating an amount of coolant in a heater loop including the heater core, transmission heating may be enabled. In particular, a position of the valves may be adjusted to enable the transmission to be sufficiently heated so that a difference between the sensed coolant temperature and transmission oil temperature is higher than a threshold amount. Only after the transmission has been sufficiently warmed, a warm-up diagnostic test of the transmission cooling and/or warming valves may be performed. Specifically, if under those conditions, a transmission oil temperature is determined to be higher than a threshold (or expected temperature), valve degradation may be indicated.
In this way, by evaluating the functionality of the valve only during conditions when the tested function is likely to provide reliable results (that is, a reliable and accurately measurable temperature difference), accuracy and reliability of the diagnostic routine can be better enabled. By not relying on data generated when the data may be unreliable and error-prone, the likelihood of a false indication of degradation may be reduced.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.